In-situ synthesis of NiS2 nanoparticles/MoS2 nanosheets hierarchical sphere anchored on reduced graphene oxide for enhanced electrocatalytic hydrogen evolution reaction.

As an important energy storage and transportation carrier, hydrogen has the advantages of high combustion heat, non-toxic, and pollution-free energy conversion process. Bimetallic sulfide composites are one of the emerging catalysts for hydrogen evolution reactions (HER) during water splitting. Herein, a hydrothermal method has been employed for the in-situ synthesis of NiS2 nanoparticles/MoS2 nanosheets (NiS2/MoS2) hierarchical sphere anchored on reduced graphene oxide (RGO) for enhanced electrocatalytic HER activity. The NiS2/MoS2/RGO composite displays improved HER activity compared to MoS2/RGO and NiS2/RGO. The optimized NiS2/MoS2/RGO-9 requires only an overpotential of 136 mV at a current density of 10 mA cm-2, a small Tafel slope of 53.4 mV dec-1, and good stability in acid solution. The synergetic effect between NiS2 nanoparticles and MoS2 nanosheets is responsible for enhanced HER performance. Moreover, RGO provides the substrate for NiS2/MoS2 species and maintains the overall conductivity of NiS2/MoS2/RGO composites. Finally, density functional theory (DFT) calculations justify and approve the efficient HER activity of NiS2/MoS2/RGO in terms of lower Gibbs free energy (0.07 eV) and lower work function (3.98 eV) that subsequently enhance the dissociation of H2O.

Ni3S2 nanostrips@FeNi-NiFe2O4 nanoparticles embedded in N-doped carbon microsphere: An improved electrocatalyst for oxygen evolution reaction.

The designing and preparing of low-cost and easily available electrocatalyst for oxygen evolution reaction (OER) are crucial for many advanced energy technologies. Herein, the Ni3S2 nanostrips@FeNi-NiFe2O4 nanoparticles embedded in N-doped carbon (Ni3S2@FeNi-NiFe2O4/C) microspheres were synthesized as improved electrocatalyst for OER, using a facile heat-treatment method. The optimized Ni3S2@FeNi-NiFe2O4/C-3 sample exhibits enhanced electrocatalytic activity toward OER performance with an overpotential of 280 mV at 10 mA cm-2 and a small Tafel slope of 33.9 mV dec-1. Furthermore, Ni3S2@FeNi-NiFe2O4/C-3 composite shows good stability in alkaline media. The outstanding electrocatalytic OER performance of composites was attributed due to the synergetic effect between Ni3S2 nanostrips and FeNi-NiFe2O4 nanoparticles and it is believed that the heterointerfaces between them act as active centers for OER. Additionally, N-doped carbon prevents the aggregation of Ni3S2@FeNi-NiFe2O4 species and enhances the conductivity of composites during the OER process.

Nitrogen-doped carbon dots modified dibismuth tetraoxide microrods: A direct Z-scheme photocatalyst with excellent visible-light photocatalytic performance.

In this work, an all solid direct Z-scheme photocatalyst of monoclinic dibismuth tetraoxide microrods/nitrogen-doped carbon dots (m-Bi2O4/NCDs) has been constructed through a simple one-step hydrothermal method. The m-Bi2O4/NCDs photocatalyst exhibits excellent photocatalytic activity for the degradation of methylene orange (MO) and phenol under visible light irradiation. The pollutants of MO (10 mg L-1) and phenol (45 mg L-1) could be efficiently degraded by m-Bi2O4/NCDs within 30 and 120 min, respectively, which is much better than that of the single m-Bi2O4, indicating that the introduction of NCDs into m-Bi2O4 can effectively improve the photocatalytic activity. Moreover, the m-Bi2O4/NCDs photocatalyst possesses a high photocatalytic stability and durability, and its photocatalytic activity did not show obvious decline after four photodegradation cycles. It is found that both O2- and direct h+ oxidation play important roles in the degradation process, and based on the experimental result a direct Z-scheme photocatalytic mechanism is proposed. This study suggests that the as-prepared m-Bi2O4/NCDs composite is a promising photocatalyst for environmental remediation.

Metal-organic framework derived Fe/Fe3C@N-doped-carbon porous hierarchical polyhedrons as bifunctional electrocatalysts for hydrogen evolution and oxygen-reduction reactions.

The development of simple and cost-effective synthesis methods for electrocatalysts of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is critical to renewable energy technologies. Herein, we report an interesting bifunctional HER and ORR electrocatalyst of Fe/Fe3C@N-doped-carbon porous hierarchical polyhedrons (Fe/Fe3C@N-C) by a simple metal-organic framework precursor route. The Fe/Fe3C@N-C polyhedrons consisting of Fe and Fe3C nanocrystals enveloped by N-doped carbon shells and accompanying with some carbon nanotubes on the surface were prepared by thermal annealing of Zn3[Fe(CN)6]2·xH2O polyhedral particles in nitrogen atmosphere. This material exhibits a large specific surface area of 182.5 m2 g-1 and excellent ferromagnetic property. Electrochemical tests indicate that the Fe/Fe3C@N-C hybrid has apparent HER activity with a relatively low overpotential of 236 mV at the current density of 10 mA cm-2 and a small Tafel slope of 59.6 mV decade-1. Meanwhile, this material exhibits excellent catalytic activity toward ORR with an onset potential (0.936 V vs. RHE) and half-wave potential (0.804 V vs. RHE) in 0.1 M KOH, which is comparable to commercial 20 wt% Pt/C (0.975 V and 0.820 V), and shows even better stability than the Pt/C. This work provides a new insight to developing multi-functional materials for renewable energy application.